TUCSON, Ariz. (AP) -- The man accused of carrying out a mass shooting in Tucson pleads not guilty in a Phoenix courtroom on Monday.

Jared Loughner, 22, entered his not guilty plea to charges he tried to kill Rep. Gabrielle Giffords and two of her aides in Monday's arraignment. Arraignments allow defendants to enter a plea to the charges against them.

During the brief proceeding, Loughner was asked to identify himself. He was then asked if he understands the charges against him. After that he entered his plea.

Experts were speculating Loughner might enter a plea of not guilty by reason of insanity. Such a plea could help Loughner avoid the death penalty. It could also mean that he would serve his sentence in a mental hospital rather than prison.

This is his second court appearance since he allegedly shot the congresswoman and 18 others.

There is still the issue of where any trial might be held. The judge overseeing the case, Judge Larry A. Burns, is based in San Diego. Arizona's federal judges recused themselves because one of Loughner's alleged victims, U.S. District Judge John Roll, was the chief federal judge for Arizona. The judges here recused themselves in order to avoid any appearance of impropriety.

A federal grand jury has already indicted Loughner on three charges -- the attempted assassination of Rep. Gabrielle Giffords and the attempted murder of two of her aides. Additional charges are expected, including one for Roll's death, and could carry the possibility of the death penalty.

Loughner is accused of opening fire at Giffords' "Congress on your Corner" event two weeks ago in a rampage that wounded 13 people and killed six others, including Roll and a 9-year-old girl who was born on Sept. 11, 2001.

Loughner later will face state charges dealing with the other victims.